Theoretical Studies on Structures, Properties and Dominant Debromination Pathways for Selected Polybrominated...

Area of Science:

• Environmental Chemistry
• Computational Chemistry

Background:

• Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants with environmental and health concerns.
• Accurate theoretical methods are crucial for understanding PBDE behavior and degradation.

Purpose of the Study:

• To evaluate and compare the suitability of B3LYP/6-311+G(d) and B3LYP/6-311+G(d)-SDD computational methods for optimizing PBDE structures.
• To investigate the electron capture abilities of PBDEs using electron affinity calculations.
• To explore the degradation mechanisms of PBDEs, focusing on debromination pathways.

Main Methods:

• Density Functional Theory (DFT) calculations using B3LYP functional with 6-311+G(d) and 6-311+G(d)-SDD basis sets.
• Relativistic effects of bromine were considered in the SDD basis set.
• Calculations included structural optimization, electron affinity, transition states, and reaction pathways for electron-induced reductive debromination.

Main Results:

• The B3LYP/6-311+G(d) method demonstrated higher accuracy for C-Br and C-O bond length optimization compared to B3LYP/6-311+G(d)-SDD.
• A strong correlation was observed between the lowest unoccupied molecular orbital (LUMO) and electron affinity, indicating its role in electron capture.
• For BDE-22, the meta-positioned bromine was found to be preferentially removed during debromination.

Conclusions:

• The B3LYP/6-311+G(d) method is recommended for accurate structural optimization of PBDEs.
• Understanding electron affinity is key to predicting PBDE electron capture abilities.
• The study provides insights into the degradation mechanisms of PBDEs, relevant for environmental remediation strategies.